The Montreal Protocol for the protection of the ozone layer mandated the phase out of the use of chlorofluorocarbons (CFCs). Materials friendlier to the ozone layer, such as hydrofluorocarbons (HFCs), e.g. HFC-134a, replaced chlorofluorocarbons. The latter compounds have proven to be greenhouse gases, causing global warming. They were regulated by the Kyoto Protocol on Climate Change. With the continued concern over global climate change there is an increasing need to develop technologies to replace those with high ozone depletion potential (ODP) and high global warming potential (GWP). Though hydrofluorocarbons (HFCs), being non-ozone depleting compounds, have been identified as alternatives to chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) as solvents, cleaning agents and heat transfer fluids, they still tend to have significant GWP. Hydrofluoroolefins (HFO) have been identified as potential alternatives with zero ODP and low GWP.
Hence, numerous documents teach processes for making such HFOs, including HFO-1234yf.
For example, WO 2007/079431 discloses processes for the production of fluorinated olefins, including hydrofluoropropenes. The processes which are broadly described as a single reaction or two or more reactions involve fluorination of a compound of the formula C(X)mCCl(Y)nC(X)m to at least one compound of formula CF3CF═CHZ, where each X, Y and Z is independently H, F, Cl, I or Br and each m is independently 1, 2 or 3 and n is 0 or 1. HFO-1234yf is prepared by fluorinating HFCO-1233xf into 1,1,1,2-tetrafluoro-2-chloropropane (HCFC-244bb), followed by dehydrochlorination. HFCO-1233xf is prepared by fluorination of the corresponding chlorinated precursor (CCl2═CClCH2Cl).
EP-A-939071 discloses, among many possibilities, gas-phase fluorination of a halogenated propene (according to a very long list) into a fluorinated propene (including in the list HFO-1234yf).
WO 2008/054781 discloses a variety of processes for producing a variety of fluoropropanes and halofluoropropenes by reacting halopropanes or halopropenes with HF, optionally in the presence of a catalyst. It discloses a process for making HFO-1234yf by reacting 2,3-dichloro-1,1,1-trifluoropropane (HCFC-243db) in the presence of HF, on a catalyst, especially Cr/Co (98/2). Reaction products comprise HFO-1234yf and HFCO-1233xf, the latter being the main product; other products are 1-chloro-3,3,3-trifluoro-1-propene (HFCO-1233zd) as well as 1,1,1,2,2-pentafluoropropane (HFC-245cb) and 1,3,3,3-tetrafluoro-1-propene (HFO-1234ze).
WO 2008/002500 discloses a process for making a mixture of HFO-1234yf and HFO-1234ze by catalytic conversion of 1,1,1,2,3-pentafluoropropane (HFC-245eb) on a dehydrofluorination catalyst.
WO 2008/040969 discloses a process comprising dehydrochlorination of HCFC-243db into HFCO-1233 (xf as well as zd), followed by a reaction involving formation of 1,1,1,2-tetrafluoro-2-chloropropane (HCFC-244bb) and later formation of the desired HFO-1234yf through dehydrochlorination. Example 1 of said document discloses a gas phase reaction at atmospheric pressure of HCFC-243db with HF on a Zn/chromia catalyst, whereby HFO-1234yf and HFCO-1233xf are formed, together with a small amount of HFC-245cb.
WO 2009/015317 discloses the reaction of a chlorinated compound which can be 1,1,2,3-tetrachloro-1-propene (HCO-1230xa), 1,1,1,2,3-pentachloropropane (HCC-240db) or 2,3,3,3-tetrachloro-1-propene (HCO-1230xf) with HF, in gas phase, on a catalyst and in the presence of at least one stabilizer. This process makes it possible to obtain 2-chloro-3,3,3-trifluoro-1-propene (HFCO-1233xf).
US 2009/0240090 discloses a process for making 2,3,3,3-tetrafluoro-1-propene (HFO-1234yf) starting from a compound of formula (I) CX2═CClCH2X, or formula (II) CX3CCl═CH2 or formula (III) CX3CHClCH2X with X=F, Cl, Br, I. The process comprises three steps, which can be followed by purification. The process includes recycling steps allowing higher conversions and yields.
WO 2010/123154 is directed to a process for producing HFO-1234yf starting from HFCO-1233xf, by reacting it with HF in the presence of oxygen and a catalyst comprising chromium oxide or fluorinated chromium oxide.
However, there is still a need to provide an improved process for making fluoroolefins such as HFO-1234yf, having in particular an improved conversion rate and/or an improved selectivity and/or which is effective over a longer period of time.